In general, cancer is the most common cause of death in the world, and this situation is similar in Korea. Cancer is caused and aggravated by genetic or environmental factors, and incidences of cancer and cancer deaths are on the rise due to changes in diet, increases in environmental contamination, increases in exposure to environmental and mental stress, and the like. As compared to other diseases, a feature of cancer is that it is relatively difficult to completely cure, and on average the survival rate after treatment is low. A feature of cancer associated with the survival rate is that there are large differences in prognosis and the survival rate depending on the progress stage of cancer. In spite of 100 years of the development of technologies for treating cancer, complete cure rates of late-stage cancer or metastatic cancer patients are significantly low (Etzioni R. et al., Nature Reviews Cancer 3, 243-252, 2003). Further, generally, there are no subjective symptoms in early stage of cancer, and in the cases in which cancer is diagnosed by subjective symptoms, frequently, cancer is already at a late stage when it is incurable. That is, in order to effectively treat cancer and increase a survival rate, there is a need to develop a method capable of diagnosing cancer at an early stage when it is curable, in addition to a method for treating cancer. To this end, research into the development of a biofactor, that is, a biomarker capable of assisting in early diagnosis of cancer, is currently actively being conducted around the world based on proteomics.
A tumor biomarker may be variously used. For example, the cancer biomarker may assist in early diagnosis of cancer and enable measurement of a progression stage of cancer, monitoring of a progression state of cancer depending on treatment, and determination of prognosis after operation (Rifai N. et al., Nature Biotech., 24, 971-983, 2006). In order to detect cancer and trace the progression state of cancer using the biomarker having the above-mentioned purposes and functions, a non-destructive method is required. Therefore, body fluids such as blood, and the like, of which examination is not dangerous, are recognized as optimal biosamples for developing the biomarker. That is, the most standardized approach for develop a cancer biomarker is to develop a biomarker capable of detecting cancer using urine, saliva, blood, or the like. Among them, blood may be the most comprehensive biosample in which proteins derived from all tissues are concentrated. Further, in view of a form of a bio material, the most preferable form of the tumor biomarker may be a protein.
Among methods for diagnosing a patient with gastric cancer, which is of the most common cancer in Korea, the most frequently used examination methods are gastroscopy, ultrasound test, and the like. However, since in these methods for gastric cancer diagnosis, expensive medical equipment is used, diagnosis costs too much, and some patients may be reluctant to undergo gastroscopy.
Due to these problems, there is a need to develop a tumor biomarker applicable to an in vitro diagnosis technology capable of detecting cancer using a small amount of body fluid, particularly, blood. At present, actually, there is no FDA approved blood-derived biomarker associated with gastric cancer.
In view that 50% or more of proteins in the body are glycoproteins, various human diseases are more likely to be associated with the glycoproteins. Therefore, it is possible to develop a diagnosis marker by screening glycoproteins associated with diseases, and analyzing disease-specific glycan structures thereof.
Most of the biochemical studies on cancer are focused on protein expression changes, but, in accordance with the development of a technology of analyzing glycan structures, glucoconjugates have become increasingly important. It is known that tumor development may be labeled with glycosylation, which is one of post-translational modification processes, but until now, accurate scientific reasons why a glycan structure is changed in tumor has not been found yet. However, these cancer-specific glycans may be released to the blood, and these glycans may be used for diagnosis by using various kinds of antibodies, and the like.
Lectins derived from plants may recognize various glycan structures. Since these lectins may be easily used, and are cheap, the lectins have been mainly used to detect glycan structures. Further, recently, methods capable of analyzing a tracer amount of glycan using an advanced mass spectrometer have been developed.